HSC 2012-2015 Chemistry Marathon (archive) (5 Viewers)

[nightweaver066]

Re: HSC 2012 Chemistry Marathon

This is the weirdest question (for Chemistry) that I've seen to date - like, it's not really HSC but LOL

Reminds me of physics; Haven't seen kWh for a while now.. haha

 

[viraj30]

Re: HSC 2012 Chemistry Marathon

This is the weirdest question (for Chemistry) that I've seen to date - like, it's not really HSC but LOL

why is it weird?? does it need more information??? if not then plz gimme an answer im curious

 

[someth1ng]

Re: HSC 2012 Chemistry Marathon

why is it weird?? does it need more information??? if not then plz gimme an answer im curious

It's fine, it's just not apart of the HSC syllabus or anything like it.

 

[viraj30]

Re: HSC 2012 Chemistry Marathon

It's fine, it's just not apart of the HSC syllabus or anything like it.

then plz i really need an answer! ohk ill show u my method and yous can tell me if im correct or not!

Energy required= mass x c x delta t
= 32 x 4180 x 20
= 2675200 Joules
1kwh= 3600000
therefore 2675200/3600000= 0.74 kwh..therefore total cost= .74*15= 11.15 cents Is my method correct???

 

[viraj30]

Re: HSC 2012 Chemistry Marathon

bump

 

[someth1ng]

Re: HSC 2012 Chemistry Marathon

Yeah, looks right to me.

 

[Kimyia]

Re: HSC 2012 Chemistry Marathon

I was wondering what the difference was between the dehydration of ethanol to ethylene and the hydration of ethylene to ethanol. Both use H2SO4 and I think dehydration uses conc. H2SO4 whereas hydration uses dilute H2SO4 but are there any other differences in the procedures? Thanks

 

[someth1ng]

Re: HSC 2012 Chemistry Marathon

I was wondering what the difference was between the dehydration of ethanol to ethylene and the hydration of ethylene to ethanol. Both use H2SO4 and I think dehydration uses conc. H2SO4 whereas hydration uses dilute H2SO4 but are there any other differences in the procedures? Thanks

Dehydration uses slightly higher temperatures (350C) and concentrated sulfuric acid OR porous ceramic crystal OR zeolite catalyst.
Hydration uses slightly lower temperatures (300C), dilute sulfuric acid OR highly acidic zeolite catalyst and high pressures.

Even with these differences, the process is rather similar and all you really need to remember is that they both have ~300C temperature and concentrated/dilute sulfuric acid catalysts. Another obvious difference is that one reaction is the reverse of the other.

Catalyst is needed in both is essentially the typical reason, very slow reaction if no catalyst is present.

 

[nightweaver066]

Re: HSC 2012 Chemistry Marathon

Question:

 

[zeebobDD]

Re: HSC 2012 Chemistry Marathon

Guys for your trends in the periodic table, i suggest you use equations when stating that the top left forms basic oxides and top right forms acidic
i.e
SO2+H20 ---> H2S03 etc etc

 

[zeebobDD]

Re: HSC 2012 Chemistry Marathon

 

[nightweaver066]

Re: HSC 2012 Chemistry Marathon

View attachment 24567

Natural systems require buffers in order to perform optimally preventing diseases and problems from arising. A buffer is an equimolar solution of weak acid and it's conjugate base that resists change in pH when small amounts of acid or base are added. A natural system in which buffers exist is human blood.

An amphiprotic substance is able to act as an acid or base (i.e. a proton donor or acceptor). A specific buffer consisting of an amphiprotic species in human blood is H2CO3/HCO3-. The buffer is vital in our blood as it maintains the pH between 7.35 - 7.45 preventing acidosis or alkylosis.

There exists a chemical equilibrium of this buffer in our blood:
H2CO3 -> HCO3- + H+

When there is excess acid in our blood, i.e. pH < 7.35, the buffer system will favour the reverse reaction in order to decrease the concentration of hydrogen ions, the equilibrium position will shift to the left and hence increase the pH.

When there is excess base in our blood, i.e. pH > 7.45, it will react with the hydrogen ions forming water:
H+ + OH- -> H2O

The system will favour the forward reaction to produce more hydrogen ions, the equilibrium position will shift to the right and hence decrease the pH.

As H2CO3/HCO3- can act as both an acid or base dependant on the changes in pH of our blood, it is an amphiprotic substance that can act as a buffer in human blood.

My questions still up there waiting for someone.

 

[barbernator]

Re: HSC 2012 Chemistry Marathon

Does anyone know the dissociation rate of sulphurous acid as a percentage at standard temp and pressure? thanks

 

[zeebobDD]

Re: HSC 2012 Chemistry Marathon

Question:

Sulfuric Acid is a diprotic strong acid. Lavoisier defined acids as a non-metal compound containing oxygen. Since H2S04 contains oxygen and isnt a metal lavoisiers theory of acids clearly accepts H2s04 as an acid. Sir Humphry Davy stated acids as substances that contain replaceable hydrogen atoms, for when they real with metals, the metals appear to replace the hydrogen in the acid causing Hydrogen gas to be evolved. H2S04 + 2Na ----> Na2S04 + H2,

The Arrhenius theory of acids stated that acids are substances that when they dissovled in water, they release hydrogen ions. When H2S04 is dissovled in H20

H2S04+ H20 ---> H30+ + HS03- therefore sulfuric acid also statisfies Svante's theory of acid. Lowry-Bronsted theory of acids(current one), states that acids are proton donors ie if a substance has a greater tendency to donate a proton than a particular solvent, then in that solvent it will be an acid. H2S04 also statisfies this given theory, as it will donate a proton when H2S04+ H20 ---> H30+ + HS03-, thus sulfuric acid can be classified as an Acid by all theories.

guys can you let me know if this will be 6 marks n what i need to do to make it better?
[/FONT]

 

[nightweaver066]

Re: HSC 2012 Chemistry Marathon

Sulfuric Acid is a diprotic strong acid. Lavoisier defined acids as a non-metal compound containing oxygen. Since H2S04 contains oxygen and isnt a metal lavoisiers theory of acids clearly accepts H2s04 as an acid. Sir Humphry Davy stated acids as substances that contain replaceable hydrogen atoms, for when they real with metals, the metals appear to replace the hydrogen in the acid causing Hydrogen gas to be evolved. H2S04 + 2Na ----> Na2S04 + H2,

The Arrhenius theory of acids stated that acids are substances that when they dissovled in water, they release hydrogen ions. When H2S04 is dissovled in H20

H2S04+ H20 ---> H30+ + HS03- therefore sulfuric acid also statisfies Svante's theory of acid. Lowry-Bronsted theory of acids(current one), states that acids are proton donors ie if a substance has a greater tendency to donate a proton than a particular solvent, then in that solvent it will be an acid. H2S04 also statisfies this given theory, as it will donate a proton when H2S04+ H20 ---> H30+ + HS03-, thus sulfuric acid can be classified as an Acid by all theories.

guys can you let me know if this will be 6 marks n what i need to do to make it better?
[/FONT]

Content sounds pretty good, expression could be better (but this isn't english so i'm not going to criticise that lol).

Lavoisier defined acids as containing oxygen as he found non-metal oxides which reacted to form acids in water, e.g. sulfuric acid. Then provide the equation of sulfur trioxide reacting with water.

Stay consistent in your response! Unsure if this is that important but you said acids dissolve to form hydrogen ions, but in your chemical equation, you had sulfuric acid forming hydronium ions.

The rest looks fine though.

Comment on my answer whether it's worthy 6 marks or not?

 

[zeebobDD]

Re: HSC 2012 Chemistry Marathon

Content sounds pretty good, expression could be better (but this isn't english so i'm not going to criticise that lol).

Lavoisier defined acids as containing oxygen as he found non-metal oxides which reacted to form acids in water, e.g. sulfuric acid. Then provide the equation of sulfur trioxide reacting with water.

Stay consistent in your response! Unsure if this is that important but you said acids dissolve to form hydrogen ions, but in your chemical equation, you had sulfuric acid forming hydronium ions.

The rest looks fine though.

Comment on my answer whether it's worthy 6 marks or not?

ahhh thankss im tryinng to improve that already let me check yours

hmm yeap that should get you the 6, though in the answers iv got they structure it out so they explain how it works as both an acid and a base then give the equations respectively underneath, but it really doesnt matter nice

 

[nightweaver066]

Re: HSC 2012 Chemistry Marathon

ahhh thankss im tryinng to improve that already let me check yours

hmm yeap that should get you the 6, though in the answers iv got they structure it out so they explain how it works as both an acid and a base then give the equations respectively underneath, but it really doesnt matter nice

Sweet, thanks for the feedback.

New question:

 

[kingkong123]

Re: HSC 2012 Chemistry Marathon

(a) The use of beta rays to gauge the thickness of cardboard is most efficient. Beta rays are able to pass through (penetrate) the cardboard, and hence be detected - determining its thickness.
(b) Geiger-Muller Counter
(c)The Geiger-Muller counter has countless advantages compared to mechanical instruments such as callipers. They minimise exposure to the radiation, hence lowering the risk of cell mutilation and cancer. They also electronically convert the readings to a simple readable value, making it easy to compare and note thickness levels.

More depth needed?

 

[zeebobDD]

Re: HSC 2012 Chemistry Marathon

NEW QUESTION:

Discuss problems associated with the use of CFCs and analyse their effect on the atmosphere using appropriate chemical equations

 

[nightweaver066]

Re: HSC 2012 Chemistry Marathon

(a) The use of beta rays to gauge the thickness of cardboard is most efficient. Beta rays are able to pass through (penetrate) the cardboard, and hence be detected - determining its thickness.
(b) Geiger-Muller Counter
(c)The Geiger-Muller counter has countless advantages compared to mechanical instruments such as callipers. They minimise exposure to the radiation, hence lowering the risk of cell mutilation and cancer. They also electronically convert the readings to a simple readable value, making it easy to compare and note thickness levels.

More depth needed?

In (a), explain what you mean by 'efficient'.

The rest is fine though.

zeebobDD, i doubt many people have started chemical monitoring and management lol.